Photometric apparatus.



No. 777,867. PATENTED DEC. 20. 1904. B. THOMSON. PHOTOMETRIG APPARATUS.

APPLIUATIQN FILED JULY 31, 1901- no MODEL. BSHIJETS-SHEET 1 InvenTonElih LL Thomson.

No. 777,867. PATENTED DEC. 20, 1904. B. THOMSON.

PHOTOMETRIG APPARATUS.

APPLICATION FILED JULY 31, 1901.

3 SHEETS-SHEET 2.

WiTnesses; Im/entor:

M W, ElLhuThomson'. M W b UNITED STATES Patented December 20, 1904.

PATENT OFFICE.

ELIHU THOMSON, OF SVVAMPSCOTT, MASSACHUSETTS, ASSIGNOR TO GENERALELECTRIC COMPANY, A CORPORATION OF NEW YORK.

PHOTOMETRIC APPARATUS- SPECIFIGATION forming part of Letters Patent No.777,867, dated December 20, 1904.

Application filed July 31, 1901. Serial No. 70,851.

To alt whom, it may concern:

Be it known that I, ELIHU THOMSON, a citizen of the United States,residing at Swampscott, county of Essex, State of Massachusetts, haveinvented certain new and useful Improvements in Photometric Apparatus,of which the following is a specification.

This invention relates to optical devices for comparing the intensitiesof light emitted from different sources.

place, and to this end the apparatus embodying my invention is soconstructed as to be light and portable. For easy transportation it ispreferably made to knock down into a compact and convenient shape.

The apparatus consists of a light-proof box in which is placed someobject to be observed, preferably a card bearing several rows of printedmatter, each row printed in type of a size different from the otherrows. The box is provided with a light-tube through which the light tobe tested is permitted to shine upon the card or other object. The boxalso has an observing-tn be through which the observer can look at thecard. By noting which size of type is legible at a given distance, firstfrom one light and then from another, he can readily determine whichlight hasthe greater intensity. The instrument is of especial value inrating electric lamps.

In the accompanying drawings, Figure 1 is perspective view of theapparatus ready for use. Fig. 2 is a similar view showing it knockeddown and packed for transportation. Fig. 3 is a longitudinal section ofthe lighttube. Fig. i is a similar section of the screen for theobserving-tube. Fig. 5 is a similar section of the observing-tube. Fig.6 is a similar section of the box with the lid thereof open. Fig. 7shows a testing-card. Fig. 8 is a perspective view of the light-tube.Fig. 9 is a similar View of the screen. Fig. 10 is a similar view of theobserving-tube. Fig. 11 is a similar view of the box.

The box A can be opened on one side, being preferably provided withahinged lid A for this purpose. At a suitable point inside the box andpreferably on the inside of the hinged Its object is to enable suchcomparison to be made at any desiredlid is a device for holding theobject to be observed, preferably a clamp for a printed card composed,for example, of two or three undercut strips B, forming a rectangularframe open on one side, so that the card C can be easily slid into theframe and removed therefrom. In the side of the box opposite the frame Bis a hole a, into which fits one end of the observing-tube D, whichpreferably tapers slightly, so that when thrust outward through saidhole the lower end will make a tight joint therein. Suitable fasteningson the box, such as spring-catches E, hold the observing-tube in place.The outer end of this tube is surrounded by a screen F, preferablydetachable and secured by spring-catches f or the like and having itsedge guarded by a fringe F of felt or fur or some other soft substance.This edge of the screen is shaped to fit snugly against the face of theobserver around his eyes. The light-tube G is inserted in a hole a inone side of the box, preferably near the observing-tube, as shown. Forconvenience the light-tube may be oblique to the side of the box, oneedge resting against a shoulder (4 The end of the tube extends into thebox and is there detachably secured, as by clamping-nuts H, meshing withscrew-studs H,pro jecting from blocks H", secured to the inside of thebox and received in longitudinal slots g in the end of the tube G. Theaxial line of the light-tube intersects the axial line of theobserving-tube at the frame B when the lid is closed, so that the lightentering through the tube will fall directly on the card C and render itlegible to the observer. The light-tube is preferably of uniformcross-section and longenough to effectually screen out substantially allrays of light other than those radiating from the lamp underobservation. The box is preferably provided with convenient means forholding it, such as a handle I, having a screw-threaded shank engagingwith a nut I, secured in one side of the box.

The mode of using the apparatus is as follows: Place a card in the frameand close the lid. Select a given size of type and go to a point so fardistant from the lamp that this type cannot be read. Direct thelight-tube toward the lamp and press the screen close to the face so asto cut out all extraneous light. Wait a few seconds until the eyesadjust themselves to the light in the box and then walk slowly backward,stopping at short intervals until a point is reached at which theselected type can be read. Note the distance from the lamp, and thenrepeat this operation for the other light or lights being compared. Bysquaring the distances the relative value of the lights will beascertained. In order to avoid any error due to familiarity with thereading matter on the card, a number of cards may be used having thesame sizes of type corresponding with the several numbers, but withdifferent reading matter, so that when changing from one lamp to anothera different card may be used for each. A less accurate test can be madeby taking a position midway between two lamps and noting the size of thetype which can be read first by the light from one lamp and then by thatfrom the other, taking care to make the reading when the are (ifarc-lamps are being tested is on the observing side.

Other modes of using this instrument will sugest themselves to thoseskilled in the art.

In order to prevent any alteration in the integrity of the surface ofthe test-cards, they may be made of some absolutely permanent material,such as porcelain, which will not darken with age or retain dust.

When the device is to be knocked down, the nuts H are removed and thelight-tube pulled out. The spring-catches f are released, allowing thescreen to be taken off the observing-tube, which is then pushed into thebox on pressing back the spring-catches E. The observing-tube, screen,handle, and nuts are then placed inside the light-tube, which is thenslid into the box, resting on blocks a, which may be covered with feltand retain the tube in place, as indicated by dotted line in Fig. 6. Thelid is then closed, and the box may be carried by a handle A secured toit, as shown in Fig. 1l,or in a casing K with straps and bands K, asshown in Fig. 2.

I am aware of the patent to Houston and Kennelly, No. 552,371, December31, 1895; but my invention differs from theirs in that it does not haveany translucent plate for diffusing the light or any focusing-eyepiece,and does have a light-tube for screening out all rays of light savethose emitted by the lamp to be tested. In the claims herewith annexed Ihave included these novel features in order to properly differentiate myinvention from that of the patent aforesaid.

WVhat I claim as new, and desire to secure by Letters Patent of theUnited States, is

1. A portable photometric apparatus, consisting of a light-tight boxprovided with a light-tube, an observing-tube, and an object to beobserved located in said box at the intersection of the axes of saidtubes.

2. A portable photometric apparatus, consisting of a light-tight boxprovided with a light-tube, an observing-tube, and means within the boxat the intersection of the axes of said tubes for removably holding anobject to be observed.

3. A portable photometric apparatus, consisting of a light-tight boxprovided with a light-tube of uniform cross-section, an observing-tube,and means for removably holding a printed card at the intersection ofthe axial lines of the two tubes.

4. A portable photometric apparatus, consisting of a light-tight boxprovided on its inside with means for holding a printed card or thelike, and an observing-tube and a lighttube both entering the same sideof said box.

5. A portable photometric apparatus, consisting of a light-tight boxprovided with a lid having on its inner suface means for holding a card,and an observing-tube and a light-tube entering the side of the boxopposite the lid.

6. A portable photometric apparatus, consisting of a light-tight boxhaving a hinged lid carrying on its inner surface undercut strips, andan observing-tube and a light-tube entering the side of the box oppositethe lid.

7. The combination with a box having a hole in one side, of a light-tubeprojecting through said hole into the box and detachably securedtherein, and an observing-tube whose axial line intersects that of thelight-tube within the box.

8. The combination with a box having a hole in one side, ofclamping-screws adjacent to said hole, a light-tube having slots in oneend to engage with said screws when the tube is inserted through saidhole, and an observingtube whose axial line intersects that of thelight-tube within the box.

9. A portable photometric apparatus, comprising a box, anobserving-tube, and a lighttube; said tubes being detachable and adaptedto pack one within the other and inside of said box.

In witness whereof I have hereunto set my hand this 29th day of July,1901.

ELII-IU THOMSON.

Witnesses:

DUGALD MoK. MoKlnLor, JoHN J. WALKER.

ITO

